The present invention relates to a cylinder head of a piston engine, having a thermal insulation component made by sintering from aluminum titanate, which has openings for valves, spark plugs or injection nozzles.
For the prevention of wall losses, it has previously been proposed in German Offenlegungsschrift No. 2,821,506 to cover the inside surface of a cylinder head with a laminated insulating plate. The laminated insulating plate described consists of the actual insulating layer and a metal backing plate tightly joined thereto. The insulating layer faces the combustion chamber and consists either of vitreous fused silica, or of silicon nitride or silicon carbide, and it is either fused or sintered onto the metal backing plate, or the insulating layer is of laminated construction with an especially porous middle layer which is formed preferably of spheres of the insulating material. In such a cylinder head it is disadvantageous that the usual arrangement of several separate openings for valves, spark plugs and injection nozzles is difficult to achieve, and consequently it is necessary to have only a single opening in the laminated insulating plate. Another disadvantage lies in the complexity of construction, especially in the fact that the actual insulating layer, on account of its low strength, requires a metal backing plate.
German Offenlegungsschrift No. 3,039,718 disclosed a cylinder head in which a refractory body consisting of silicon nitride is inserted into a thermal insulation component consisting of aluminum titanate, and this laminate is shrink-fitted into a metal supporting body, which in some cases is formed by the cylinder head. The refractory body, which forms the bottom of the cylinder head, faces the combustion chamber and protects the thermal insulation component against mechanical stress. The thermal insulation component is in the form of a circular disk having a marginal rim to accommodate the refractory body. Here, again, the disadvantage is the laminated construction of the individual components consisting of different materials, which is necessitated by the low strength of aluminum titanate. Another disadvantage is that the laminate consisting of the thermal insulation component and the refractory body takes up additional space in the cylinder head and thereby interferes with the complex configurations of the coolant passages. Another disadvantage results from the fact that the cylinder head cannot be sealed against the barrel of the cylinder in the area of the aluminum titanate component, so that the sealing is performed on the refractory body whose thermal conductivity is good, with the disadvantage that a heat bridge is formed. Sealing outside of the laminated component of aluminum titanate is not possible, because, for reasons of design, the valve bores must run all the way to the edge of the component. Since aluminum titanate has a low modulus of elasticity, it is necessary to heat the cylinder head to a relatively high temperature in order to shrink-fit the laminate, and this must be considered an additional disadvantage.
It is the object of the present invention to overcome the existing disadvantages and, for the achievement of a satisfactory insulating effect in the cylinder head, to make available a thermal insulation component which can be inserted into the cylinder head, without the formation of heat bridges to the cylinder head or motor block, and which furthermore is of simple construction and low height, so that the formation of coolant passages is not impaired, at least in this critical region adjacent the combustion chamber. Furthermore the thermal insulation component is to have sufficient strength to resist mechanical forces, especially pressures.
It is a further purpose of the invention to provide for a firm seating of the component in the cylinder head, and at the same time to develop a simple method of installing the thermal insulation component. In particular, the invention intends to make it possible for the thermal insulation component to be locked in place without the need for a refractory body on the thermal insulating component to protect it against the pressure forces that occur.